CRTH2 is a G-protein coupled 7th transmembrane domain molecule cloned by Nagata et al. in 1999 as a molecule expressed selectively on Th2 cells (see Non Patent Document 1).
It has been reported that the Th2 cell is one form of activated T cells and induces production of IgE from B cells via production of cytokines such as IL-4, IL-5, and IL-13 (see Non Patent Document 2). Furthermore, it has been reported that the cytokines induce the activation of eosinophil and basophil (see Non Patent Documents 3 and 4). From the above reports, it has been believed that the Th2 cells are strongly involved in the formation of pathologic conditions of allergic diseases such as asthma, allergic rhinitis, and atopic dermatitis directly or indirectly via other cells or factors (see Non Patent Document 5).
Because CRTH2 is cloned as a molecule expressed selectively on the Th2 cell as mentioned above, and also, it has relatively high homology to a chemokine receptor (see Non Patent Document 6), it has been assumed that CRTH2 is involved in immune responses or immune-related disorders. Thereafter, it has been revealed that CRTH2 is expressed in eosinophil and basophil in addition to the Th2 cell, and that the ligand is PGD2 and the action thereof induces a cell migration reaction and the like (see Non Patent Document 7). In particular, it has been suggested that CRTH2 is involved in allergic diseases.
In addition to such in vitro tests, in exacerbation of symptoms in an asthma model by a CRTH2-specific ligand and in a dermatitis model (see Non Patent Document 8), suppression of symptoms in dermatitis in a CRTH2 defective mouse (see Non Patent Document 9), increase in expression of CRTH2 in human patients with allergic rhinitis (Non Patent Document 10), and the like, the possibility that CRTH2 is involved in allergic diseases such as asthma, atopic dermatitis, and allergic rhinitis has been reported. From such information, the possibility of creation of therapeutic agents for the above-mentioned diseases, which have a mechanism of inhibiting CRTH2, has been suggested.
Conventionally, as CRTH2 inhibitors, indolyl acetic acid derivatives (see Patent Document 1), phenoxy acetic acid derivatives (see Patent Document 2), pyrimidinyl acetic acid derivative (see Patent Document 3) and the like have been reported. However, a compound having the structure of the present invention has not been disclosed. Furthermore, although a compound of which the structure is similar to that of the compound of the present invention has been reported, there is neither description nor suggestion that such compounds have a CRTH2 inhibitory effect (see Patent Document 4).